Abstract
The increase in cerebral blood flow (CBF) with hypoxia is greater in fetal than adult sheep. Baseline CBF and oxygen delivery (OD=CBF × arterial O2 content) are also higher in the fetal sheep despite a rate of cerebral O2 consumption (CMRO2) equal to that in the adult. Previous work showed that this relative overperfusion of the fetal brain is in part due to the left shifted position of the O2-hemoglobin dissociation curve (ODC) in the fetus. 6 unanesthetized fetal sheep were studied to determine if the greater response of CBF to hypoxia in the fetus is also dependent upon the position of the ODC. Measurements of blood gases, CBF (microsphere technique), CMRO2, OD, and the reciprocal of the arteriovenous (brachiocephalic a. - sagittal sinus) difference in O2 content (1/CaO2-CvO2) were made at 3 levels of CaO2 pre and postexchange transfusion (ET) with adult blood. 1/CaO2-CvO2=CBF/CMRO2 measures changes in CBF if CMRO2 remains stable and is less subject to error than micro-sphere CBF measurements. P50 increased from 16.6 ± 0.5 - 31.7 ± 1.9 Torr (±SEM) and OD decreased 13.12 ± 1.56 - 6.63 ± 0.34 ml·100g−1·min−1 with ET (p < .05). During hypoxia, CMRO2 was unchanged both pre and post ET. The response of 1/CaO2-CvO2 to hypoxia was steeper pre ET (p <.05). These data support the role of the position of the ODC in the regulation of CBF during hypoxia and are consistent with a tissue O2 dependent mechanism of CBF control.
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Rosenberg, A., Harris, A. & Jones, M. 1499 ROLE OF O2-HEMOGLOBIN AFFINITY ON THE RESPONSE TO HYPOXIA OF CEREBRAL BLOOD FLOW IN THE FETAL SHEEP. Pediatr Res 19, 360 (1985). https://doi.org/10.1203/00006450-198504000-01523
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DOI: https://doi.org/10.1203/00006450-198504000-01523
